Abstract

This paper presents part of the work done within the project 'Advanced Numerical Simulation and Performance Evaluation of WAM-V® in Spray Generating Conditions' developed by the International Center for Numerical Methods in Engineering (CIMNE) under Navy Grant N62909-12-1-7101 issued by the Office of Naval Research Global. One of the primary goals of that project was the development of a computational model for simulation of the Wave Adaptive Modular Vessel (WAM-V®) under spray generating conditions. For this purpose, a Semi-Lagrangian Particle Finite Element Method (SL-PFEM) has been applied. This is the latest development within the framework of the so-called Particle Finite Element Method (PFEM), using the X-IVAS (eXplicit Integration along the Velocity and Acceleration Streamlines) scheme. In this paper we demonstrate the applicability of the SL-PFEM using the X-IVAS scheme for the simulation of the Wave Adaptive Modular Vehicle under spray generating conditions.

Abstract

The aim of this work is to be able to cope with complex sloshing-seakeeping problems in an effective manner. For this purpose, two different solvers will be integrated into one coupled tool to take advantage of their characteristics.

The Particle Finite Element Method is a versatile framework for the analysis of fluid-structure interaction problems. The latest development within the framework of the PFEM is the X-IVAS (eXplicit Integration along the Velocity and Acceleration Streamlines) scheme. It is a semi-implicit scheme built over a Semi-Lagrangian (SL) formulation. This new scheme was named PFEM-2 and will be used in this work to solve the fluid dynamics (sloshing) inside the tanks.

The PFEM-2 will be coupled in the time domain with SeaFEM, a solver developed for seakeeping problems. SeaFEM solves the second-order diffraction-radiation equations by using the Finite Element Method (FEM) and will be used in this work to simulate the interaction between waves and a floating body.

The coupling of the two tools will be accomplished by using an effective coupling algorithm and a communication technique that allows simulations to be computed without affecting the global compute time and the accuracy of the solvers. This new tool has been validated against experimental benchmarks carried out in a model basin at model scale.

Abstract

A Wave Adaptive Modular Vessel (WAM-V®) is a new class of ship that uses inflatable flexible hulls to conform to the surface of the water. It is similar in design to a catamaran, in that it has a twin hull design and no keel. However, the superstructure is not rigidly attached to the hulls; it uses shock absorbers and ball joints to articulate the vessel, which allows WAM-V to conform to the surface of the water while mitigating the stresses transmitted to the structure. Moreover, the inflatable hulls help to absorb the high frequency wave-loads. These features allow WAM-V to travel efficiently with low wave resistance in rough seas, by surfing on top of the waves rather than cut through them.

The objective of the WAM-V is to be a lightweight watercraft capable of moving fast and efficiently on the surface of the sea. WAM-Vs are designed to allow for a variety of applications for either manned or unmanned operations and can be built in different lengths to match specific services.

This presentation shows part of the work done in the project ‘Advanced Numerical Simulation and Performance Evaluation of WAM-V ® in Spray Generating Conditions’ developed by the International Center for Numerical Methods in Engineering (CIMNE) under Navy Grant N62909-12-1-7101 issued by the Office of Naval Research Global. The scope of that project included the performance analysis of the WAM-V in waves, taking into account the flexibility of the ship hulls, using fluid-structure interaction computational models. However, the focus of this paper is one of the primary concerns of that project; the development of a computational model for simulation of the WAM-V under spray generating conditions. In this regards, the final goal was to develop and demonstrate a computational engineering solver that could be used to design strategies to reduce the spray generation of the vessel.

Abstract

In this work, a second-order semi-Lagrangian particle finite element method (SL-PFEM) is presented. The method is based on the second order velocity Verlet algorithm, using an explicit scheme to integrate the particles’ trajectories, and an implicit Crank-Nicholson scheme to integrate the particle’s velocities. The projection of the particle´s intrinsic variables onto the finite element (FE) mesh is based on a second-order global least-square. The elliptic part of the Navier-Stokes equations is discretized with the Crank-Nicholson scheme and solved using an iterative process. The method is verified against available analytical solutions, and applied to the classic flow around a cylinder problem.